CBC · California Building Code

What special inspections apply to soil improvement, shoring and vibro stone columns?

If your project uses soldier‑pile/tie‑back shoring or vibro stone columns, the CBC requires specific special inspections: shoring follows § 1705A.6.2 and the inspection/monitoring rules in § 1812A (tie‑back testing, load cells, surveys, records), while vibro stone columns follow § 1705A.6.3 and the detailed geotechnical, testing and Final Verified Report requirements in § 1813A (including minimum 2‑ft diameter, ≤8‑ft spacing, CPT/SPT acceptance criteria, and FVR before foundations).

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Last reviewed: July 5, 2026

What the code requires — 2–4 sentences

The California Building Code requires that earth‑retaining shoring be subject to special inspections and tests as directed by § 1705A.6.2, which delegates the detailed inspection and monitoring requirements to Section 1812A. Vibro stone columns (VSCs) used for ground improvement are likewise subject to special inspection and testing per § 1705A.6.3 and must comply with the provisions of Section 1813A (including the construction‑document and TIO requirements of § 1813A.5).

Requirements in detail

Where the authority in the CBC points

Special inspection requirement cites: § 1705A.6.2 (earth‑retaining shoring → Section 1812A) and § 1705A.6.3 (vibro stone columns → Section 1813A.5).
Statement of special inspections: the registered design professional must prepare the statement of special inspections identifying scope and whether inspections are continuous or periodic (§ 1704A.3).

Earth‑retaining shoring (summary of the inspection obligations)

§ 1705A.6.2 requires special inspections and tests for earth‑retaining shoring in accordance with applicable portions of Section 1812A. § 1812A then prescribes inspection, testing and monitoring scope (soldier piles, tie‑back anchors, load cells, survey monitoring, records, tolerances, etc.).
Key inspection activities required by 1812A include: periodic site visits by the shoring design engineer, special inspector/geotechnical observation of tie‑back anchor installation and testing, monitoring of adjacent existing structures, maintaining complete records of soldier pile and anchor installation, and verification/calibration of test equipment.

Vibro stone columns (summary of the inspection obligations)

§ 1705A.6.3 requires that special inspections and tests for vibro stone columns follow Section 1813A.5. Section 1813A (general, geotechnical report, installation, testing, and construction‑document requirements) sets the mandatory inspection, field verification and Final Verified Report (FVR) requirements. Foundation work cannot commence until the FVR is submitted and approved.
The geotechnical report must specify acceptance criteria and the required field verification testing methods (CPT, SPT, friction/piezocone criteria) and must specify the required special inspection/observation by the geotechnical engineer. A Final Verified Report documenting compliance is required.

Decision‑relevant dimensions and values (code excerpts)

Item	Typical decision/value	Code reference
Minimum VSC diameter	2 ft (minimum)	§ 1813A.2.4
Maximum VSC center‑to‑center spacing	8 ft (maximum)	§ 1813A.2.4
Extent of ground improvement beyond foundation footprint	½ depth of VSCs, minimum 10 ft beyond footprint (or approved alternative)	§ 1813A.2.3
VSC aggregate size	Maximum 6 in; gradation limits noted in § 1813A.4	§ 1813A.4
Required field acceptance tests for VSCs	CPT (ASTM D5778) ± SPT (ASTM D1586) as specified in geotech report	§ 1813A.2.7
Final Verified Report (FVR) before foundation construction	FVR required and must be submitted/approved before foundation work begins	§ 1813A.2.9 and § 1813A.5.6
Shoring — load cell spacing (monitoring)	Load cells at max 50 ft intervals; min one per wall	§ 1812A (monitoring requirements)
Shoring — load cell reading frequency	Once per day during excavation; once per week during remainder	§ 1812A monitoring (tie‑back load cells)
Tie‑back anchor performance testing	Test at ≥2 × design load; production anchors tested at 150% of design, not to exceed specified tensile limits; creep tests where required	§ 1812A.4.1 (testing requirements)
Soils/fill special inspection (general)	Some soil activities require continuous geotechnical observation; others periodic — see Table 1705A.6	§ 1705A.6 (Table and 1705A.6.1)

(These are the mandatory minima appearing in the cited sections. The geotechnical report or the registered design professional may require additional testing/inspection.)

How inspections are designated (continuous vs periodic)

The statement of special inspections must identify whether an item is continuous or periodic; Table 1705A.6 shows examples for soils/fills (continuous observation during placement of compacted fill, periodic verification of subgrade, compaction testing, etc.). § 1704A.3 and Table 1705A.6.

Exceptions & special cases

Section 1812A applies only where existing or new facilities are affected; shoring used purely as construction means/methods that do not affect existing/new facilities is not regulated by this section (but remains subject to jurisdictional requirements).
Vibro stone column provisions in Section 1813A apply to unbonded (non‑grouted) aggregate columns for shallow foundations and explicitly do NOT apply to grouted/bonded stone columns, ground improvement for deep foundations, or to changing site class. VSCs are not considered deep foundations.
For both shoring and VSCs, the geotechnical report and the registered design professional’s construction documents can require more stringent inspection/testing than the minimum code provisions; those project documents drive the scope of the actual special inspections. § 1705A.7 notes use of approved geotechnical report and project documents to determine compliance.

Common mistakes

Treating VSCs as isolated foundation elements rather than requiring the improvement to be installed under the entire building footprint (Section 1813A requires installation under the entire footprint).
Beginning foundation construction before the Final Verified Report (FVR) for ground improvement is submitted and approved (required by § 1813A.5).
Omitting required monitoring details from the statement of special inspections — the RDP must identify type/extent and whether continuous or periodic per § 1704A.3.
Failing to implement monitoring/surveying of adjacent structures or to keep the preconstruction photographic/log records required for shoring monitoring in § 1812A.7.
Assuming standard compaction testing alone is sufficient for VSC acceptance — the geotechnical report must specify CPT/SPT acceptance criteria in accordance with § 1813A.2.7.

Worked example — applying the rule with numbers

Scenario: A one‑story commercial building will be supported on a shallow mat foundation over vibro stone‑improved soils. The geotechnical engineer proposes VSCs 20 ft deep, 2 ft diameter, in a square grid at 8‑ft spacing.

What the code requires and what inspectors will do:

Check that the minimum diameter and spacing meet the code minima: 2 ft dia and ≤ 8 ft spacing — acceptable per § 1813A.2.4.
Extent beyond footprint: half the VSC depth = 10 ft; code minimum extent beyond footprint is 10 ft, so the proposed 10 ft meets the minimum per § 1813A.2.3.
Construction documents must include: size, depth, locations of VSCs; locations of CPT/SPT verification; TIO program; and a note that foundation work shall not begin until the FVR is approved (§ 1813A.5). The special inspector will confirm that those items are on the construction documents.
During installation the geotechnical special inspector will witness/record the CPT/SPT testing and/or friction cone tests and compare results to the acceptance criteria specified in the geotechnical report (§ 1813A.2.7 and § 1813A.2.8). Once the TIO program is complete and acceptance criteria are met, the geotechnical engineer issues the FVR; only then may foundation construction proceed (§ 1813A.2.9 and § 1813A.5.6).

Related provisions

§ 1705A.6.2 — Special inspections of earth‑retaining shoring (delegates to § 1812A).
§ 1812A — Earth‑retaining shoring (inspection, survey monitoring, tolerances, tie‑back testing).
§ 1812A.6 / § 1812A.7 — Inspection, testing and monitoring requirements for shoring, monitoring frequency and preconstruction logs.
§ 1705A.6.3 — Special inspections for vibro stone columns (delegates to § 1813A.5).
§ 1813A.1–.5 — Vibro stone column requirements: geotechnical report, sizing/spacing, installation, testing/verification, construction‑document and FVR requirements.
§ 1704A.3 — Statement of special inspections (content, designation of continuous/periodic).

Code references

Grounded in the retrieved California Building Code — click a citation to read the verbatim passage:

CBC § 1705A.6 High relevance — show source text

TABLE 1705A.6—REQUIRED SPECIAL INSPECTIONS AND TESTS OF SOILS	Col2	Col3
TYPE	CONTINUOUS SPECIAL INSPECTION	PERIODIC SPECIAL INSPECTION
1. Verify materials below shallow foundations are adequate to achieve the design bearing capacity.	—	X
2. Verify excavations are extended to proper depth and have reached proper material.	—	X
3. Perform classification and testing of compacted fill materials.	—	X
4. During fill placement, verify use of proper materials and procedures in accordance with the provisions of the approved geotechnical report. Verify densities and lift thicknesses during placement and compaction of compacted fill.	X	—
5. Prior to placement of compacted fill, inspect subgrade and verify that site has been prepared properly.	—	X

1705A.6.1 Soil fill. All fills used to support the foundations of any building or structure shall be continuously inspected by the geotechnical engineer or his or her qualified representative. It shall be the responsibility of the geotechnical engineer to verify that fills meet the requirements of the approved construction documents and to coordinate all fill inspection and testing during construc- tion involving such fills.

The duties of the geotechnical engineer or his or her qualified representative shall include, but need not be limited to, the inspec- tion of cleared areas and benches prepared to receive fill; inspection of the removal of all unsuitable soils and other materials; the approval of soils to be used as fill material; the inspection of placement and compaction of fill materials; the testing of the completed fills; and the inspection or review of geotechnical drainage devices, buttress fills or other similar protective measures in accordance with the approved construction documents.

A verified report shall be submitted by the geotechnical engineer as required by the California Administrative Code. The report shall indicate that all tests and inspections required by the approved construction documents were completed and whether the tested materials and/or inspected work meet the requirements of the approved construction documents.

1705A.6.2 Earth-retaining shoring. Special inspections and tests of earth-retaining shoring shall be in accordance with applicable portions of Section 1812A.

1705A.6.3 Vibro stone columns. Special inspections and tests of vibro stone columns for ground improvement shall be in accordance with Section 1813A.5.

1705 A .7 Driven deep foundations. Special inspections and tests shall be performed during installation of driven deep foundation elements as specified in 1810A.3.3.1.2 and Table 1705 A .7. The approved geotechnical report and the construction documents prepared by the registered design professionals shall be used to determine compliance.

TABLE 1705A.7—REQUIRED SPECIAL INSPECTIONS AND TESTS OF DRIVEN DEEP FOUNDATION ELEMENTS	Col2	Col3
TYPE	CONTINUOUS SPECIAL INSPECTION	PERIODIC SPECIAL INSPECTION
1. Verify element materials, sizes and lengths comply with the requirements.	X	—
2.

CBC § 1705A.6.2 High relevance — show source text

1705A.6.2 Earth-retaining shoring. Special inspections and tests of earth-retaining shoring shall be in accordance with applicable portions of Section 1812A.

1705A.6.3 Vibro stone columns. Special inspections and tests of vibro stone columns for ground improvement shall be in accordance with Section 1813A.5.

TABLE 1705A.7—REQUIRED SPECIAL INSPECTIONS AND TESTS OF DRIVEN DEEP FOUNDATION ELEMENTS	Col2	Col3
TYPE	CONTINUOUS SPECIAL INSPECTION	PERIODIC SPECIAL INSPECTION
1. Verify element materials, sizes and lengths comply with the requirements.	X	—
2. Determine capacities of test elements and conduct additional load tests, as required.	X	—
3. Inspect driving operations and maintain complete and accurate records for each element.	X	—
4. Verify placement locations and plumbness, confirm type and size of hammer, record number of blows per foot of penetration, determine required penetrations to achieve design capacity, record tip and butt elevations and document any damage to foundation element.	X	—
5. For steel elements, perform additional special inspections in accordance with Section 1705_A_.2.	In accordance with Section 1705_A_.2	In accordance with Section 1705_A_.2
6. For concrete elements and concrete-filled elements, perform tests and additional special inspections in accordance with Section 1705_A_.3.	In accordance with Section 1705_A_.3	In accordance with Section 1705_A_.3
7. For specialty elements, perform additional inspections as determined by the registered design professional in responsible charge.	In accordance with Statement of Special Inspections	In accordance with Statement of Special Inspections

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SPECIAL INSPECTIONS AND TESTS

1705A.7.1 Driven deep foundations observation. The installation of driven deep foundations shall be continuously observed by a qualified representative of the geotechnical engineer responsible for that portion of the project.

The representative of the geotechnical engineer shall make a report of the deep foundation pile-driving operation giving such pertinent data as the physical characteristics of the deep foundation pile-driving equipment, identifying marks for each deep founda- tion pile, total depth of embedment for each deep foundation; and when the allowable deep foundation pile loads are determined by a dynamic load formula, the design formula used, and the permanent penetration under the last 10 blows. One copy of the report shall be sent to the enforcement agency.

CBC § 18A-28 High relevance — show source text
Monitoring shall be performed by a licensed surveyor and shall consist of vertical and lateral_ movement of the existing structures. Prior to starting shoring installation a preconstruction meeting shall take place between the contractor, shoring design engineer, surveyor, geotechnical engineer and building official to identify monitoring locations on existing buildings. 6. If in the opinion of the building official or shoring design engineer, monitoring data indicate excessive movement or other distress, all excavation shall cease until the geotechnical engineer and shoring design engineer investigate the situation and make recommendations for remediation or continuing. 7. All readings and measurements shall be submitted to the building official and shoring design engineer.

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SOILS AND FOUNDATIONS

1812A.8 Tolerances. The following tolerances shall be specified on the construction documents. 1. Soldier piles: a. Horizontal and vertical construction tolerances for the soldier pile locations. b. Soldier pile plumbness requirements (angle with vertical line).

2. Tie-back anchors:

a. Allowable deviation of anchor projected angle from specified vertical and horizontal design projected angle. b. Anchor clearance to the existing/new utilities and structures.

SECTION 1813A—VIBRO STONE COLUMNS FOR GROUND IMPROVEMENT

1813A.1 General. This section shall apply to vibro stone columns (VSCs) for ground improvement using unbounded aggregate materials. Vibro stone column provisions in this section are intended to increase bearing capacity, reduce settlements and mitigate liquefaction for shallow foundations. These requirements shall not be used for grouted or bonded stone columns, ground improvement for deep founda- tion elements or changing site class. VSCs shall not be considered a deep foundation element. Ground improvement shall be installed under the entire building/structure footprint and not under isolated foundation elements only. Design, construction, testing and inspec- tion shall satisfy the requirements of this code except as modified in Sections 1813A.2 through 1813A.5.

1813A.2 Geotechnical report. The geotechnical report shall specify vibro stone column requirements to ensure uniformity in total and differential immediate settlement, long term settlement and earthquake induced settlement. 1. Soil compaction shall be in accordance with California Geological Survey (CGS) Special Publication 117A (SP-117A): Guidelines for Evaluating and Mitigating Seismic Hazard in California. 2. Area replacement ratio for the compaction elements and the basis of its determination shall be explained. Minimum factor of safety for soil compaction shall be in accordance with SP-117A. 3. Depth of soil compaction elements and extent beyond the footprint of structures/foundation shall be defined. Extent beyond the foundation shall be half the depth of the VSCs with a minimum of 10 ft or an approved alternative. 4. Minimum diameter and maximum spacing of soil compaction elements shall be specified. VSCs shall not be less than 2 feet in diameter, and center to center spacing shall not exceed 8 feet. 5. The modulus of subgrade reactions for shallow foundations shall account for the presence of compaction elements. 6. The modulus of subgrade reactions, long-term settlement and post-earthquake settlement shall be specified along with expected total and differential settlements for design. _7.
CBC § 1813A.2 High relevance — show source text
1813A.2 Geotechnical report. The geotechnical report shall specify vibro stone column requirements to ensure uniformity in total and differential immediate settlement, long term settlement and earthquake induced settlement. 1. Soil compaction shall be in accordance with California Geological Survey (CGS) Special Publication 117A (SP-117A): Guidelines for Evaluating and Mitigating Seismic Hazard in California. 2. Area replacement ratio for the compaction elements and the basis of its determination shall be explained. Minimum factor of safety for soil compaction shall be in accordance with SP-117A. 3. Depth of soil compaction elements and extent beyond the footprint of structures/foundation shall be defined. Extent beyond the foundation shall be half the depth of the VSCs with a minimum of 10 ft or an approved alternative. 4. Minimum diameter and maximum spacing of soil compaction elements shall be specified. VSCs shall not be less than 2 feet in diameter, and center to center spacing shall not exceed 8 feet. 5. The modulus of subgrade reactions for shallow foundations shall account for the presence of compaction elements. 6. The modulus of subgrade reactions, long-term settlement and post-earthquake settlement shall be specified along with expected total and differential settlements for design. 7. The acceptance criteria for Friction Cone and Piezocone Penetration Testing in accordance with ASTM D5778 complemented by the standard penetration test (SPT) in accordance with ASTM D1586, if necessary, to verify soil improvement shall be specified. 8. The requirements for special inspection and observation by the geotechnical engineer shall be specified. 9. A final verified report (FVR) documenting the installation of the ground improvement system and confirming that the ground improvement acceptance criteria have been met shall be prepared by the geotechnical engineer and submitted to the enforce- ment agency for review and approval.

1813A.3 Shallow foundations. VSCs under the shallow foundation shall be located symmetrically around the centroid of the footing or load.

1. There shall be a minimum of four stone columns under each isolated or continuous/combined footing or approved equivalent. 2. The VSCs shall not be used to resist tension or overturning uplift from the shallow foundations. 3. The foundation design for the shallow foundation shall consider the increased vertical stiffness of the VSCs as point supports for analysis, unless it is substantiated that the installation of the VSCs result in improvement of the surrounding soils such that the modulus of subgrade reaction, long term settlement and post-earthquake settlement can be considered uniform throughout.

1813A.4 Installation. VSCs shall be installed with vibratory probes. Vertical columns of compacted unbounded aggregate shall be formed through the soils to be improved by adding gravel near the tip of the vibrator and progressively raising and repenetrating the vibrator which will results in the gravel being pushed into the surrounding soil. Gravel aggregate for VSCs shall be well graded with a maximum size of 6 inches and not more than 10 percent smaller than [3] / 8 inch after compaction.
CBC § 1812A.7 High relevance — show source text
Supple-_ mental shoring shall be devised to eliminate further movement and the building official shall review and approve the supplemental shoring before excavation continues. 11. Monitoring of tie-back anchor loads: a. Load cells shall be installed at the tie-back heads adjacent to buildings at maximum interval of 50 feet, with a minimum of one load cells per wall. b. Load cell readings shall be taken once a day during excavation and once a week during the remainder of construction. c. Load cell readings shall be submitted to the geotechnical engineer, shoring design engineer, engineer in responsible charge and building official. d. Load cell readings can be terminated once the temporary shoring no longer provides support for the buildings.

1812A.7 Monitoring of existing structures. 1. The contractor shall complete a written and photographic log of all existing structures within 100 ft or three times depth of shoring, prior to construction. A licensed surveyor shall document all existing substantial cracks in adjacent existing structures. 2. The contractor shall document existing condition of wall cracks adjacent to shoring walls prior to start of construction. 3. The contractor shall monitor existing walls for movement or cracking that may result from adjacent shoring. 4. If excessive movement or visible cracking occurs, the contractor shall stop work and shore/reinforce excavation and contact the shoring design engineer and building official. 5. Monitoring of the existing structure shall be at reasonable intervals as required by the registered design professional subject to approval of the building official. Monitoring shall be performed by a licensed surveyor and shall consist of vertical and lateral movement of the existing structures. Prior to starting shoring installation a preconstruction meeting shall take place between the contractor, shoring design engineer, surveyor, geotechnical engineer and building official to identify monitoring locations on existing buildings. 6. If in the opinion of the building official or shoring design engineer, monitoring data indicate excessive movement or other distress, all excavation shall cease until the geotechnical engineer and shoring design engineer investigate the situation and make recommendations for remediation or continuing. 7. All readings and measurements shall be submitted to the building official and shoring design engineer.

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1812A.8 Tolerances. The following tolerances shall be specified on the construction documents. 1. Soldier piles: a. Horizontal and vertical construction tolerances for the soldier pile locations. b. Soldier pile plumbness requirements (angle with vertical line).

2. Tie-back anchors:

a. Allowable deviation of anchor projected angle from specified vertical and horizontal design projected angle. b. Anchor clearance to the existing/new utilities and structures.

SECTION 1813A—VIBRO STONE COLUMNS FOR GROUND IMPROVEMENT
CBC § 1704.5 High relevance — show source text
At completion of fabrication, the approved fabricator shall submit a certificate of compliance to the owner or the owner’s authorized agent for submittal to the building official as specified in Section 1704.5 stating that the work was performed in accordance with the approved construction documents.

1704.3 Statement of special inspections. Where special inspections or tests are required by Section 1705, the registered design professional in responsible charge shall prepare a statement of special inspections in accordance with Section 1704.3.1 for submittal by the applicant in accordance with Section 1704.2.3.

Exception: The statement of special inspections is permitted to be prepared by a qualified person approved by the building official for construction not designed by a registered design professional.

1704.3.1 Content of statement of special inspections. The statement of special inspections shall identify the following:
1. The materials, systems, components and work required to have special inspections or tests by the building official or by the registered design professional responsible for each portion of the work.
2. The type and extent of each special inspection.
3. The type and extent of each test.
4. Additional requirements for special inspections or tests for seismic or wind resistance as specified in Sections 1705.12, 1705.13 and 1705.14.
5. For each type of special inspection, identification as to whether it will be continuous special inspection, periodic special inspection or performed in accordance with the notation used in the referenced standard where the inspections are defined.
6. Deferred submittal items that require a supplemental statement of special inspections.
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SPECIAL INSPECTIONS AND TESTS

1704.3.2 Seismic requirements in the statement of special inspections. Where Section 1705.13 or 1705.14 specifies special inspections or tests for seismic resistance, the statement of special inspections shall identify the designated seismic systems and seismic force-resisting systems that are subject to the special inspections or tests. [OSHPD 1R, 2 & 5] Where Section 1705.13 or 1705.14 specifies special inspections or tests for seismic resistance, the statement of special inspections shall identify the equip- ment/components that require special seismic certification and seismic force-resisting systems that are subject to the special inspection or tests.

1704.3.3 Wind requirements in the statement of special inspections. Where Section 1705.12 specifies special inspection for wind resistance, the statement of special inspections shall identify the main windforce-resisting systems and wind-resisting components that are subject to special inspections.

1704.4 Contractor responsibility. Each contractor responsible for the construction of a main wind- or seismic force-resisting system, designated seismic system or a wind- or seismic force-resisting component listed in the statement of special inspections shall submit a written statement of responsibility to the building official and the owner or the owner’s authorized agent prior to the commencement of work on the system or component. The contractor’s statement of responsibility shall contain acknowledgement of awareness of the special requirements contained in the statement of special inspections.
CBC § 2.0 High relevance — show source text
3. Maximum recommended anchor tension capacity based upon the soil or rock strength/grout bond and anchor depth/spacing. 4. Allowable bond stress at the ground/grout interface and applicable factor of safety for ultimate bond stress for the anchor. For permanent anchors, a minimum factor of safety of 2.0 shall be applied to the ground soil interface as required by PTI Recommendations for Prestressed Rock and Soil Anchors Section 6.6.

5. Minimum grout pressure for installation and post-grout pressure for the anchor. The presumptive post-grout pressure of 300 psi may be used for all soil types. 6. Class I corrosion protection is required for all permanent and extended temporary anchors in service more than 2 years. A minimum of Class II corrosion protection is required for temporary anchors in service less than or equal to 2 years. 7. Performance test for the anchors shall be at a minimum of two times the design loads and shall not exceed 80 percent of the specified minimum tensile strength of the anchor rod. A creep test is required for all prestressed anchors that are perfor- mance tested. All production anchors shall be tested at 150 percent of design loads and shall not be greater than 70 percent of the specified minimum tensile strength of the anchor rod. 8. Earth pressure, surcharge pressure and the seismic increment of earth pressure loading, when applicable. 9. Maximum recommended lateral deformation at the top of the soldier pile, at the tie-back anchor locations and the drilled pier concrete shafts at the lowest grade level. 10. Allowable vertical soil bearing pressure, friction resistance and lateral passive soil resistance for the drilled pier concrete shafts and associated factors of safety for these allowable capacities. 11. Soil-pier shaft/pile interaction assumptions and lateral soil stiffness to be used in design for drilled pier concrete shaft or pile lateral loads.

12. Acceptable drilling methods. 13. Geotechnical observation and monitoring recommendations.

1812.4.2 Structural requirements : 1. Tendons shall be thread-bar anchors conforming to ASTM A722. 2. Anchor design loads shall be based upon the load combinations in Section 2.4 of ASCE 7 and shall not exceed 60 percent of the specified minimum tensile strength of the tendons. 3. The anchor shall be designed to fail in grout bond to the soil or rock before pullout of the soil wedge. 4. Design of shoring system shall account for as-built locations of soil anchors considering all specified construction tolerances in Section 1812.8

5. Design of shoring system shall account for both short- and long-term deformation.

1812.4.3 Testing of tie-back anchors : 1. The geotechnical engineer shall keep a record at the job site of all test loads and total anchor movement and report their

accuracy. 2. If a tie-back anchor initially fails the testing requirements, the anchor shall be permitted to be re-grouted and retested. If the anchor continues to fail, the followings steps shall be taken: a. The contractor shall determine the cause of failure: (variations of the soil conditions, installation methods, materials, etc.).
CBC § 1813.2 High relevance — show source text
Ground improvement shall be installed under the entire building/structure footprint and not under isolated foundation elements only.

Design, construction, testing and inspection shall satisfy the requirements of this code except as modified in Sections 1813.2 through 1813.5.

1813.2 Geotechnical report. The geotechnical report shall specify vibro stone column requirements to ensure uniformity in total and differential immediate settlement, long-term settlement and earthquake-induced settlement. The report shall address the following: 1. Soil compaction shall be sufficient to mitigate potential for liquefaction as described in California Geological Survey (CGS) Special Publication 117A (SP-117A): Guidelines for Evaluating and Mitigating Seismic Hazard in California. 2. The area replacement ratio for the compaction elements and the basis of its determination shall be explained. Minimum factor of safety for soil compaction shall be in accordance with SP-117A. 3. The depth of soil compaction elements and extent beyond the footprint of structures/foundation shall be defined. Extent beyond the foundation shall be half the depth of the VSCs with a minimum of 10’ or an approved alternative. 4. The minimum diameter and maximum spacing of soil compaction elements shall be specified. VSCs shall not be less than 2 feet in diameter and center to center spacing shall not exceed 8 feet. 5. The modulus of subgrade reactions for shallow foundations shall account for the presence of compaction elements.

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SOILS AND FOUNDATIONS

6. The modulus of subgrade reactions, long-term settlement and post-earthquake settlement shall be specified along with expected total and differential settlements for design. 7. The acceptance criteria for friction cone and piezocone penetration testing in accordance with ASTM D5778 complemented by a standard penetration test (SPT) in accordance with ASTM D1586, if necessary, to verify soil improvement shall be specified 8. The requirements for special inspection and observation by the geotechnical engineer shall be specified. 9. A Final Verified Report (FVR) documenting the installation of the ground improvement system and confirming that the ground improvement acceptance criteria have been met shall be prepared by the geotechnical engineer and submitted to the enforce- ment agency for review and approval.

1813.3 Shallow Foundations. VSCs under the shallow foundation shall be located symmetrically around the centroid of the footing or load, and:

1. There shall be a minimum of four stone columns under each isolated or continuous/combined footing or an approved equivalent. 2. The VSCs or deep foundation elements shall not be used to resist tension or overturning uplift from the shallow foundations. 3. The foundation design for the shallow foundation shall consider the increased vertical stiffness of the VSCs as point supports for analysis, unless it is substantiated that the installation of the VSCs results in improvement of the surrounding soils such that the modulus of subgrade reaction, long-term settlement and post-earthquake settlement can be considered uniform throughout.
CBC § 1813A.3 High relevance — show source text
if necessary, to verify soil improvement shall be specified._ 8. The requirements for special inspection and observation by the geotechnical engineer shall be specified. 9. A final verified report (FVR) documenting the installation of the ground improvement system and confirming that the ground improvement acceptance criteria have been met shall be prepared by the geotechnical engineer and submitted to the enforce- ment agency for review and approval.

1813A.3 Shallow foundations. VSCs under the shallow foundation shall be located symmetrically around the centroid of the footing or load.

1. There shall be a minimum of four stone columns under each isolated or continuous/combined footing or approved equivalent. 2. The VSCs shall not be used to resist tension or overturning uplift from the shallow foundations. 3. The foundation design for the shallow foundation shall consider the increased vertical stiffness of the VSCs as point supports for analysis, unless it is substantiated that the installation of the VSCs result in improvement of the surrounding soils such that the modulus of subgrade reaction, long term settlement and post-earthquake settlement can be considered uniform throughout.

1813A.4 Installation. VSCs shall be installed with vibratory probes. Vertical columns of compacted unbounded aggregate shall be formed through the soils to be improved by adding gravel near the tip of the vibrator and progressively raising and repenetrating the vibrator which will results in the gravel being pushed into the surrounding soil. Gravel aggregate for VSCs shall be well graded with a maximum size of 6 inches and not more than 10 percent smaller than [3] / 8 inch after compaction.

1813A.5 Construction documents. Construction documents for VSCs, as a minimum, shall include the following: 1. Size, depth and location of VSCs. 2. Extent of soil improvements along with building/structure foundation outlines. 3. Field verification requirements and acceptance criteria using CPT/SPT. 4. The locations where CPT/SPT shall be performed. 5. The testing, inspection and observation (TIO) program shall indicate the inspection and observation required for the VSCs. 6. A note indicating foundation construction shall not commence until the final verified report specified in Section 1813A.2 Item 9 has been submitted to and approved by the enforcement agency.

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CALIFORNIA BUILDING CODE – MATRIX ADOPTION TABLE

CHAPTER 19 – CONCRETE

(Matrix Adoption Tables are nonregulatory, intended only as an aid to the code user. See Chapter 1 for state agency authority and building applications.)

CBC § 1705.8 High relevance — show source text

TABLE 1705.8—REQUIRED SPECIAL INSPECTIONS AND TESTS OF CAST-IN-PLACE DEEP FOUNDATION ELEMENTS	Col2	Col3
TYPE	CONTINUOUS SPECIAL INSPECTION	PERIODIC SPECIAL INSPECTION
1. Inspect drilling operations and maintain complete and accurate records for each element.	X	—
2. Verify placement locations and plumbness, confirm element diameters, bell diameters (if applicable), lengths, embedment into bedrock (if applicable) and adequate end-bearing strata capacity. Record concrete or grout volumes.	X	—
3. For concrete elements, perform tests and additional special inspections in accordance with Section 1705.3.	In accordance with Section 1705.3	In accordance with Section 1705.3

1705.9 Helical pile foundations. Continuous special inspections shall be performed during installation of helical pile foundations. The information recorded shall include installation equipment used, pile dimensions, tip elevations, final depth, final installation torque and other pertinent installation data as required by the registered design professional in responsible charge. The approved

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SPECIAL INSPECTIONS AND TESTS

geotechnical report and the construction documents prepared by the registered design professional shall be used to determine compliance.

1705.10 Structural integrity of deep foundation elements. Whenever there is a reasonable doubt as to the structural integrity of a deep foundation element, an engineering assessment shall be required. The engineering assessment shall include tests for defects performed in accordance with ASTM D4945, ASTM D5882, ASTM D6760 or ASTM D7949, or other approved method.

1705.11 Fabricated items. Special inspections of fabricated items shall be performed in accordance with Section 1704.2.5.

1705.12 Special inspections for wind resistance. Special inspections for wind resistance specified in Sections 1705.12.1 through 1705.12.3, unless exempted by the exceptions to Section 1704.2, are required for buildings and structures constructed in the following areas:

In wind Exposure Category B, where basic wind speed, V, is 150 mph (67 m/sec) or greater.
In wind Exposure Category C or D, where basic wind speed, V, is 140 mph (62.6 m/sec) or greater.

1705.12.1 Structural wood. Continuous special inspection is required during field gluing operations of elements of the main windforce-resisting system. Periodic special inspection is required for nailing, bolting, anchoring and other fastening of elements of the main windforce-resisting system, including wood shear walls, wood diaphragms, drag struts, braces and hold-downs.

Exception: Special inspections are not required for wood shear walls, shear panels and diaphragms, including nailing, bolting, anchoring and other fastening to other elements of the main windforce-resisting system, where the lateral resistance is provided by structural sheathing and the specified fastener spacing at panel edges is more than 4 inches (102 mm) on center.

CBC § 8.4 High relevance — show source text
15. If a tie-back anchor initially fails the testing requirements, the anchor shall be permitted to be regrouted and retested. If anchor continues to fail, the followings steps shall be taken: a. The contractor shall determine the cause of failure—variations of the soil conditions, installation methods, materials,

etc.

b. The contractor shall propose a solution to remedy the problem. The proposed solution will need to be reviewed and approved by the geotechnical engineer, shoring design engineer and building official. 16. After a satisfactory test, each anchor shall be locked-off in accordance with Section 8.4 of PTI Recommendations for Prestressed Rock and Soil Anchors.

1812A.6 Inspection, survey monitoring and observation. 1. The shoring design engineer or his designee shall make periodic visits to the job site for the purpose of observing the installa- tion of shoring system, testing of tie-back anchors and monitoring of survey. 2. Testing, inspection and observation shall be in accordance with testing, inspection and observation requirements approved by the building official. The following activities and materials shall be tested, inspected or observed by the special inspector and geotechnical engineer: a. Sampling and testing of concrete in soldier pile and tie-back anchor shafts. b. Fabrication of tie-back anchor pockets on soldier beams c. Installation and testing of tie-back anchors. d. Survey monitoring of soldier pile and tie-back load cells. e. Survey monitoring of existing buildings.

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SOILS AND FOUNDATIONS

3. A complete and accurate record of all soldier pile locations, depths, concrete strengths, tie-back locations and lengths, tie-back grout strength, quantity of concrete per pile, quantity of grout per tie-back and applied tie-back loads shall be maintained by the special inspector and geotechnical engineer. The shoring design engineer shall be notified of any unusual conditions encountered during installation. 4. Calibration data for each test jack, pressure gauge and master pressure gauge shall be verified by the special inspector and geotechnical engineer. The calibration tests shall be performed by an independent testing laboratory and within 120 calendar days of the data submitted. 5. Monitoring points shall be established at the top and at the anchor heads of selected soldier piles and at intermediate intervals as considered appropriate by the geotechnical engineer. 6. Control points shall be established outside the area of influence of the shoring system to ensure the accuracy of the monitoring readings. 7. The periodic basis of shoring monitoring, as a minimum, shall be as follows: a. Initial monitoring shall be performed prior to any excavation. b. Once excavation has begun, the periodic readings shall be taken weekly until excavation reaches the estimated subgrade elevation and the permanent foundation is complete. c. If performance of the shoring is within established guidelines, shoring design engineer may permit the periodic readings to be bi-weekly. Once initiated, bi-weekly readings shall continue until the building slab at ground floor level is _completed and capable of transmitting lateral loads to the permanent structure.

Frequently asked questions

Who prepares the Statement of Special Inspections for VSCs and shoring?

The registered design professional in responsible charge prepares the Statement of Special Inspections identifying the required special inspections and whether they are continuous or periodic (§ 1704A.3).

Can foundation construction start before the vibro stone column Final Verified Report is submitted?

No. Section 1813A requires a Final Verified Report documenting acceptance of the ground improvement; the construction documents must note that foundation construction shall not commence until that FVR is submitted and approved.

Are vibro stone columns considered deep foundations?

No. Section 1813A explicitly states VSCs shall not be considered deep foundation elements and are limited to shallow‑foundation ground improvement.

How often must tie‑back anchor load cells be read during excavation?

Load cell readings at tie‑back heads must be taken once per day during excavation and once per week during the remainder of construction, with load cells installed at a maximum interval of 50 ft (minimum one per wall) as required in Section 1812A.

What tests are prescribed to verify VSC performance?

The geotechnical report must specify acceptance criteria using friction cone/piezocone testing (ASTM D5778) and complementary SPT (ASTM D1586) if necessary; the TIO program must identify where those tests are performed (§ 1813A.2.7 and § 1813A.5).

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Related in the CBC

What special inspections/tests are required for deep foundations (driven, cast-in-place, helical)?

When must a geotechnical representative continuously observe pile installation?

How is the structural integrity of deep foundation elements verified when defects are suspected?

Foundations & Soils — Required Inspections and Testing

California Building Code